The invention relates to from a fuel injection pump German Offengungsschrift 2,522,374 discloses a fuel injection pump having recesses which defines connecting cross-sections in the circumferential surface of the pump plunger, which recesses, starting at the outlet ports of the relief channel, extend towards the side of the pump working chamber. Rectangular recesses, inter alia, have been proposed which have a width differing from one another in the peripheral direction of the pump plunger and, furthermore, also differ in their axial extension, their length. With such an arrangement, during the course of an opening stroke of the pump plunger, a bent cross-sectional profile is to be achieved in such a way that, after initially restricted relief via one of the connecting ports, the relief cross-section is enlarged by the arrival of the second connecting port. In the connect-control cross-sections provided here, the restricting action occurring at different speeds of the fuel injection pump is especially emphasized. These control cross-sections are provided in particular for adaption of the fuel injection quantity as a function of the speed. Here, one of the connecting cross-sections is regularly constructed in the manner of a restricting slot.
In internal combustion engines working with spontaneous ignition, it is necessary for the low-load range, in particular the idling range, for the fuel to be introduced into the combustion chamber with exact timing but long spray duration so that so called knocking of the internal combustion engine, especially noticeable in this area, is prevented. The long duration of the injection ensures that the fuel quantity introduced during the ignition lag does not become too large and thus not too much fuel is burnt suddenly, which would lead to a steep pressure rise causing knocking. In order to achieve a long injection duration, many proposals are already known which predominantly have the feature in common that, during the duration of the delivery, a portion of the fuel delivered under high pressure is introduced into a discharge chamber which is defined by a movable wall. This means considerable expense, the discharge volume in addition having to be controlled for the various operating ranges of the internal combustion engine.